1. Field
Embodiments generally relate to a method to evaluate the pinholes of a dielectric film in a thin film transistor (TFT) structure.
2. Description of the Related Art
In recent years there has been growing interest in thin film transistors (TFTs) and devices incorporating such TFTs, such as flat panel displays, all types of integrated circuits and replacements for mechanical switches and relays. Many TFTs, such as metal oxide semiconductor TFTs, are very sensitive to hydrogen, oxygen and water in terms of device stability and repeatability.
Metal oxide semiconductor TFTs are very sensitive to hydrogen and water in terms of device stability and repeatability. The active layer (i.e., the metal oxide semiconductor layer) should be protected by an etch stop layer (e.g., for ES or etch stop-TFTs), and a passivation layer for back channel etch TFT (e.g., BCE TFT) during and/or after the TFT fabrication process. It is believed that pinholes of the dielectric layer are a major path for H2 and/or water penetration. Pinholes in the dielectric layer are believed to allow water and H2 to penetrate through the etch stop layer and/or the passivation layer toward the active layer (i.e., the metal oxide semiconductor).
In order to detect pinhole formation in a passivation layer, scanning electron microscope (SEM) studies have been performed at points after HF etching of the dielectric layer. SEM studies use a focused beam of high-energy electrons to generate a variety of signals to produce a high magnification image of the surface of a substance, such as a passivation layer. However, SEM studies have drawbacks that are not easily overcome. First, it is difficult for an SEM to look at wide range of films since SEM is generally applied for high magnification. Second, SEM cannot differentiate between a pinhole in a film and a sponge like porous film after etching.
Thus, there is a need for improved methods of determining pinhole formation.